The mishap happened on Guthni Barauni road under Guthni police station of Siwan district a little before midnight last night, Station house officer (SHO) of Guthni Mohammed Akbar said.
Those killed on the spot have been identified as Passi (35), Chandan Singh (22), Mantoo Gaur (22) and Umakamkar (60), the SHO said.
The victims were returning from a 'Tilak' ceremony when their car collided head on with another vehicle near Balaur village last night, the SHO added.
Two of the seriously injured have been referred to Patna, Akbar said.